Immunosuppressive therapy can produce hematologic improvement in a large proportion of patients with severe aplastic anemia. Antithymocyte globulin (ATG) is the current treatment of choice for patients who do not have histocompatible sibling donors or who are otherwise ineligible for allogeneic bone marrow transplant. About 50 percent of patients respond to an initial course of ATG, and many nonresponders can be salvaged by subsequent treatment with cyclosporin A (CsA). To determine whether simultaneous administration of these agents can further improve response rates, we are actively enrolling patients in a therapeutic trial of 4 days of ATG and 11 months of CsA. We have enrolled 102 patients, with a maximum followup of approximately 6 1/2 years. The results from the first 55 patients were published: Rosenfeld SJ, Kimball J, Vining D, Young NS. Superior results of combination immunosuppressive therapy with antithymocyte globulin and cyclosporin A in the treatment of severe aplastic anemia. Blood 1995;85:3058-65. More recently, the results of the first 73 enrollees were presented at the meeting of the American Society of Hematology this past December: Rosenfeld SJ, Kimball J, Young NS. Long-tenn outcomes after treatment of severe aplastic anemia with antithymocyte globulin and cyclosporin. Blood 1995;86:477a.